Firefighters were on the scene trying to figure out exactly what happened to the building under construction located at 2727 West 33rd Avenue, which is at the intersection of Clay Street.

A passerby reported the collapse just before 7 p.m.

CBS4 learned the building was a two-story apartment building that was being renovated. Denver Fire Department officials said they don’t know what renovations were being done.

Neighbors said that construction crews have spent the last several months digging out the basement of the building. One neighbor said she heard the loud collapse and when she came outside she says the street was filled with a cloud of dust.

Nobody was inside at the time of the collapse and no firefighters have been injured.